1. Field of the Invention
The present invention relates to a wireless access communication system, and more particularly to a method and apparatus for transmitting a control message from a base station to a terminal.
2. Description of the Related Art
When the quality of a signal received by a terminal from a BS (Base Station) currently providing service (hereinafter, referred to as “current serving BS”) is degraded in a wireless access communication system, a handover is performed so that the terminal receives a better quality of service from an adjacent BS (hereinafter, referred to as “new serving BS”). In this case, the terminal must replace various types of CIDs (Connector Identifiers) assigned from the current serving BS with CIDs (hereinafter, referred to as “new CIDs”) to be used in the new serving BS according to the IEEE (Institute of Electrical and Electronics Engineers) 802.16e standard. For example, the CIDs to be replaced can include a basic CID, primary management CID, secondary management CID and transport CID.
When a handover session is initiated, the new serving BS assigns, to a handover target terminal, new CIDs to be used within the new serving BS. Moreover, the new serving BS receives, from the current serving BS, information of CIDs (hereinafter, referred to as “old CIDs”) used by the terminal. Subsequently, the new serving BS maps the new CIDs to the old CIDs and transmits a result of the mapping to the terminal. Such information transmitted to the terminal is referred to as CID update information. Conventionally, the new serving BS includes the update information in a registration response message (hereinafter, referred to as “REG_RSP message”) serving as one of control messages in the form of TLV (Type-Length-Value) parameters, and transmits the REG_RSP message to the terminal.
FIG. 1 shows the format of a part of the REG_RSP message for transferring conventional CID update information, and, as an example, shows the format of a part used for transferring update information of one CID in the REG_RSP message according to the IEEE 802.16e standard. The REG_RSP message for transferring the CID update information includes an 8-byte CID update information field 10 into which the update information of one CID is inserted; and a variable-length connection information field 12 into which connection information corresponding to the CID update information inserted into the CID update information field 10 is inserted. The CID update information field 10 includes a 1-byte type field 14 into which type information of a new CID is inserted; a 1-byte length field 16 into which length information of the new CID is inserted; a 2-byte new CID field 18 into which a value of the new CID is inserted; a 1-byte type field 20 into which type information of an old CID is inserted; a 1-byte length field 22 into which length information of the old CID is inserted; and a 2-byte old CID field 24 into which a value of the old CID is inserted.
One terminal uses a plurality of CIDs. Whenever the number of CIDs is increased by one, the CID update information field 10 and the connection information field 12 associated therewith are added, one by one, in the REG_RSP message for transferring the CID update information. For example, assuming that the average number of CIDs used by one terminal is 16, 16 CID update information fields 10 are required to transfer the CID update information through the REG_RSP message whenever a handover is performed. Thus, a data field of 128 bytes (=8 bytes×16) is required for the CID update information fields.
To reduce power consumption of the terminal, the wireless access communication system uses a sleep mode indicating a standby state of the terminal as opposed to an active mode indicating a state in which the terminal is in use. That is, to reduce power consumption, the terminal is controlled so that it operates in the sleep mode when in the standby state.
When data to be transmitted to a terminal operating in the sleep mode is present, the BS transmits traffic indication information to a corresponding terminal using a traffic indicator message (hereinafter, referred to as “TRF_IND” message) that is one of control messages, thereby controlling the corresponding terminal so that it operates in the active mode.
Therefore, the BS includes, in the TRF_IND message, a BCID (Basic CID) of the terminal associated with data to be transmitted by the BS among terminals operating in the sleep mode, and broadcasts the TRF_IND message. While a predetermined sleep interval and a predetermined listening interval repeat, the terminal operating in the sleep mode wakes up for some time in the listening interval and then confirms the TRF_IND message broadcast from the BS. That is, the terminal determines whether or not its own BCID has been included in the TRF_IND) message received from the BS. If so, the corresponding terminal wakes up from the sleep mode and then is switched to the active mode.
FIG. 2 shows the format of the conventional TRF_IND message, and more particularly shows the format of the TRF_IND message based on the IEEE 802.16e standard. The conventional TRF_IND message includes an 8-bit management message type field 30 into which management message type information is inserted; an 8-bit field 32 into which information indicating the number of positive subscriber terminals is inserted; and 16-bit BCID fields 34 to 36 into which a BCID of at least one positive subscriber terminal is inserted. The management message type information indicates a type of message to be currently transmitted. When the management message type information is “47” according to the IEEE 802.16e standard, a corresponding message is the TRF_IND message. The positive subscriber terminal indicates a terminal to which the BS transmits data. Each BCID includes a BCID value of each positive subscriber terminal.
As described above, the TRF_IND message includes information indicating the number of positive subscriber terminals, and a number of BCIDs that equal the number of positive subscriber terminals. For example, when the number of positive subscriber terminals is 6, the TRF_IND message includes 6 BCIDs. In this case, a data field of 96 bits (=16 bits×6) is required to identify the positive subscriber terminals.